Cathode ray apparatus



p 1934- W. R. BULLXMORE Er AL 1,973,606

CATHODE RAY APPARATUS Filed Dec. 29, 1932 INVENTORS William R. BullimorePatented Sept. 11, 1934 PATENT OFFICE CATHODE RAY APPARATUS WilliamRichard Bullimore and Leslie Herbert Bedford, Highbury Grove, England,'assignors to C. Cossor Limited, land,

Highbury Grove, Enga company of Great Britain Application December 29,1932, Serial No. 649,400 In Great Britain January 29, 1932 4 Claims.(Cl. 250-275) This invention relates to electrical discharge apparatusand more particularly to cathode ray oscillographs, televising tubes,relays and like apparatus in which the electrical discharge is pro- 5duced in the form of a beam capable of being deflected by anelectrostatic or electro-magnetic control.

The object of the invention is to provide improvements in theconstruction and operation of apparatus of the kind referred to and moreparticularly to increase the sensitiveness of apparatus in which thecathode rays are deflected by the electrostatic influence of controlelectrodes located within the envelope, to facilitate the manufacture ofthe apparatus and to increase the working frequency limit.

One improvement according to the invention applicable to apparatus ofthe kind referred to and in which the cathode rays are deflected by theelectrostatic influence of control electrodes enclosed within theenvelope consists in the provision of a conductive shield or screen forscreening or protecting the control electrodes from electrons reflectedor emitted from the fluorescent screen or electrode upon which thecathode rays are focussed. The effect of this screen is to eliminate orminimize the discharge which would otherwise take place between thecontrol. electrodes due to the action of secondary electrons.

The shield or screen therefore increases the sensitiveness of theapparatus by reducing the load on the input circuit.

A further improvement according to the invention applicable to apparatusof the kind referred to in which cathode rays are deflected by theelectrostatic influence of control electrodes disposed within theenvelope consists in mounting the electrodes upon a star-shaped foot orpinch formed at the end of a re-entrant tube to through which thelead-in conductors pass into the evacuated envelope. This constructionen= ables the electrodes to be assembled as a unit carried by there-entrant tube and also enables the conductor supports to be wellseparated so as as to improve the insulation thereof.

The invention consists also in an electrical discharge apparatus of thekind referred to in which the deflection of the cathode rays is effectedeither by electrostatic or electro-magnetic action '30 wherein a fillingof a light gas such as helium is employed for bringing the cathode raysto a focus. It has been customary in cathode ray tubes to employ a smallquantity of a heavy gas, such as argon, to effect focussing so as tosecure 5 the greatest focussing efiect for a. given pressure.

but we have discovered that a light gas such as helium is effective forfocussing and greatly increases the operating frequency limit of theapparatus as compared with apparatus in which aheavy gas is used.

In order that the invention may be more readily understood an example ofan oscillograph or televising tube constructed inaccordance with theinvention will now be particularly described with reference to theaccompanying drawing in which:--

Figure 1 is an elevation, partly in section, of the electrode system,

Figure 2 is a fragmentary elevation partly in section taken at rightangles to Figure 1,

Figure 3 is a sectional view on the line 3,3 of Figure 1 showing thestar-shaped pinch and Figure 4 is a plan view in which all theelectrodes with the exception of the control electrodes are omitted forthe purpose of enabling the dis- '35 position of the control electrodesin relation to the star-shaped pinch to be seen.

The apparatus shown in the accompanying drawing is of the known typecomprising an electron emitting hot cathode 1, a perforated anode 2, aninsulated tubular iocussing shield 3 surrounding the cathode and twopairs of parallel rectangular control electrodes or deflector plates 4:and 5 set at right angles to one another and embracing the cathodestream which issues from the central aperture in the anode 2, atdilierent distances from the anode. The cathode stream is focussed uponasuitable fluorescent screen (not shown) and is controlled by theelectrostatic action of the electrodes 4 and 5 in known manner so thatthe light spot produced from the fluorescent screen by the action of thecathode stream moves in accordance with the control potentials impressedon the electrodes 4 and 5.

In the operation of known discharge apparatus employing an electrodesystem of this type there is a tendency for electrons reflected oremitted from thefluorescent screen to be collected by the controlelectrodes with the result that current due to these electrons flows inthe input circuits.

In accordance with the present invention a conductive shield or screenconnected to the anode or otherwise held at a suitable positivepotential isprovided for the purpose of protecting the controlelectrodes from these secondary electrons. As shown in the drawing, theconductive shield or screen takes the form of an openended metalcylinder 6 mounted directly on the anode 2 which is provided with aflange 2a for this purpose. This cylinder surrounds the controlelectrodes and extends from the anode 2 towards the fluorescent; screenas shown so as to be capable of collecting the secondary electronsbefore they can reach the control electrodes. The cylinder is preferablyprovided with atransverse partition 7 which acts as a barrier tointercept secondary electrons which might otherwise pass down throughthe cylinder 6 and reach the control electrodes. The partition 7 isprovided with a central aperture 8 of sufllcient diameter to permit ofthe passage of the cathode stream. The cylinder 6 and partition 7 alsoact as an electrostatic screen for protecting the control electrodesfrom.the effects of glass charges.

In an alternative construction, the interior of the envelope ismetalised by any suitable known process to form a conductive coatingwhich is connected to the anode or otherwise held at a suitable positivepotential so that secondary electrons reflected or emitted from thefluorescent screen are attracted to the coating and thereby preventedfrom reaching the control electrodes. This coating may take the place ofthe screen 6 shown in the drawing.

In order to facilitate the manufacture of the apparatus and to improvethe insulation between the lead-in conductors to the several electrodes,in accordance with the present invention the electrode system is mountedupon a star-shaped foot or pinch 9 formed at the end of the re-entranttube 10 through which the lead-in conductors pass into the envelope 11.This construction enables the electrode system to be assembled as a unitcarried by the re-entrant tube and also enables the conductor supportsto be well separated since the star-shape of the pinch is well adaptedto enable the rectangularly arranged electrodes 4 and 5 to be carried onwidely spaced conductor supports.

In the preferred construction according to the invention and asillustrated in the drawing the cathode 1 is supported on two conductorsupports in sealed into two opposite arms of the starshaped pinch andconnected each to a suitable lead-in conductor as shown, whilst thefocussing shield 3 is carried on two conductor supports 3a which aresealed into the other two opposite arms of the star-shaped pinch and oneof which is connected to a suitable leading-in conductor. The anode 2carrying the cylinder 6 is supported directly on the focussing shield 3,a disc 12 of mica or other suitable insulating material, provided with acentral aperture in register with the aperture in the anode, beinginterposed between the anode 2 and the focussing shield 3. The anode isfastened to the focussing shield by means of bolts and nuts or othersuitable fastening devices 13 which pass through the anode 2 and disc12. The bolts also pass through an annular disc 14 of mica or othersuitable insulating material additional to the disc 12 and having itsouter edge engaging within a flange 2a depending from the periphery ofthe anode and its inner edge clamped between a flange 3b formed on theend of the focussing shield and a flange 15a formed on the end of a tube15 which is telescoped into the focussing tube, as shown in Figure 1 ofthe drawing, and secured by spot welding or otherwise. Current is led tothe anode by means of a conductor 16 which is welded to the flange 2aand is sealed into the reentrant tube at a point below the pinch asshown at 17 in Figure 1.

Each of the control electrodes or deflector plates 4 and 5 is supportedat one .end by a coning discs 12 and 14. Moreover they are convenientlysituated for supporting the two pairs of parallel deflector plates 4 and5 at right angles to one another as illustrated in Figure 4.

The cylinder 6 carried on the anode is preferably formed with pressedout ears or projections 20 which engage against the walls of theenvelope, as illustrated in Figure 1 of the drawing, to hold thecylinder 6 and anode 2 against transverse movement.

The envelope 11 may be fllled with any suitable gas for the purpose offocussing the cathode stream. However, if a heavy gas such as argon isemployed as is usual in cathode ray tubes of this character,difficulties will be experienced owing to the sluggishness of thefocussing effect in reestablishing itself after a disturbance of thebeam due to a rapid change of potential on the control electrodes, andthe apparatus will be unable to respond fully to waves whose frequencyis above a certain limit. We have discovered that adequate focussing ofthe cathode rays can be effected by filling the envelope with a lightgas such as helium and that the rapidity of the re-establishment of thefocussing effect is greatly increased when such a light gas is employed.In

accordance with our invention therefore, we prefer to provide a flllingof helium or other light inert gas instead of the heavy gas which hasbeen employed heretofore for focussing purposes.

It will be understood that, although the invention has been describedwith reference to the accompanying drawing as applied to a cathode ray'oscillograph or televising tube employing a fluorescent screen, theinvention is not limited to this particular application but can beapplied to any apparatus in which cathode rays focussed by the action ofa gaseous filling are deflected by electrostatic or electromagneticcontrol.

,We claim:

1. A cathode ray tube comprising a sealed envelope having a reentranttube; a substantially star shaped pinch formed on the end of saidreentrant tube and having a plurality of radiating arms; a pair ofconductor supports sealed into two different arms of said pinch; acathode connected to and supported by said conductor supports, a

second pair of conductor supports sealed into two different arms of saidpinch; a tubular focussing shield connected to and carried by saidsecond pair of conductor supports and surrounding said cathode, saidfocussing shield having an open end; a plate shaped perforated anodesecured to the open end of said focussing shield; an insulatorinterposed between said anode and said shield, said anode and insulatorhaving at least one pair of openings, at least one pair of conductorsupports sealed into two different arms of said pinch and projectingthrough said openings, and a plurality of control electrodes connectedto and carried by said last mentioned conductor supports, said insulatorengaging and locating said last mentioned conductor supports relativelyto said anode.

2. A cathode ray tube comprising a sealed envelope having a reentranttube provided on its end with a pinch of substantially a star-shape, aplurality of conductor supports sealed into said pinch, an electronemitting cathode carried by a pair of said conductor supports, afocusing shield surrounding said cathode and carried by a second pair ofsaid conductor supports, a plate shaped anode supported by said focusingshield, said anode having an opening for the passage of electronsemitted by said cathode and a plurality of apertures spaced from saidopening, a disc of insulating material between said focusing shield andsaid anode and having a plurality of apertures aligned with but ofsmaller area than those of said anode, and a plurality of controlelectrodes supported by a third series of said conductor supports, saidthird series of conductor supports extending through the apertures ofsaid anode and insulating disc and mechanically supported by said disc.

3. A cathode ray tube comprising a sealed envelope having a reentranttube; a substantially cross-shaped pinch formed on the end of saidreentrant tube and having pairs of arms in crossed relation; a pair ofconductor supports sealed into one pair of said arms of said pinch, acathode connected to and supported by said conductor supports, a secondpair of conductor supports sealed into another pair of the arms of saidpinch;

an open-ended tubular focusing shield surrounding said cathode andconnected to and carried by said second pair of conductor supports; aplate shaped anode secured to the open end of said focusing shield, saidanode having an opening for the passage of electrons emitted by saidcathode and a pair of apertures spaced from said opening, an insulatorbetween said anode and said shield and having a pair of aperturesaligned with but of smaller area than those of said anode, a third pairof conductor supports sealed into a pair of the arms. of said pinch andextending through the apertures of said anode and insulator, a pluralityof control electrodes connected to and carried by said last mentionedconductor supports, said insulator engaging and locating said lastmentioned conductor supports relatively to said anode, and a metallicshield electrically connected to said anode and surrounding said controlelectrodes.

4. A cathode ray tube according to claim 3, wherein the focusing screencomprises a pair of metallic cylinders fitted one within the other, eachof said cylinders having at its end adjacent the anode a flange providedwith a pair of apertures aligned with but of larger area than those ofthe insulating disc.

WILLIAM RICHARD BULLIMORE. LESLIE HERBERT BEDFORD.

